JP 2013-125685 A discloses a conventional illumination device. The illumination device includes a light source and a light guide plate. The light guide plate has one surface, on which multiple dot patterns are provided. Light from the light source enters one side of the light guide plate, travels through the light guide plate, and reaches the other side of the light guide plate. During this process, parts of the light are reflected by the dot patterns and exit from an opposite surface (a light emitting surface), which is opposite to the one surface mentioned above, to the outside. An area on the opposite surface side is illuminated with the exiting light. Further, JP 2013-125685 A indicates that, in order to obtain uniformity of the luminance of the light emitting surface, the density of the dot patterns provided on the one surface is changed according to the distance from the light source.